This invention relates to an apparatus for use with electronic article surveillance ("EAS") systems, and, in particular, to an apparatus for activating and/or deactivating EAS tags used in such systems.
In the field of electronic article surveillance, EAS tags which incorporate some type of magnetic sensor assembly are placed on merchandise such as audio or video tape cassettes (compact discs) to prevent unauthorized removal of the tape cassettes from a store. In a first type of EAS tag, the magnetic sensor assembly includes a magneto-mechanical active element which mechanically vibrates to generate a detectable signal at the frequency of an applied interrogation signal. In a second type of EAS tag, the magnetic sensor assembly includes a soft magnetic active element which generates a detectable signal at a harmonic of the frequency of the applied interrogation signal.
In both types of EAS tags, the magnetic sensor element also includes a hard or semi-hard magnetic biasing element. By changing the magnetic state of this biasing element, the active element of the tag is enabled or disabled from generating the detectable signal, thereby activating or deactivating the tag.
In the case of a magneto-mechanical tag, the biasing element is magnetized along its longer length dimension by a permanent magnet to activate the tag. By either degaussing the biasing element along its length or magnetizing it along its shorter width dimension, the tag is deactivated. In the case of a harmonic tag, when the biasing element is demagnetized, the tag is activated. By magnetizing the biasing element along its longer length dimension, the tag is then deactivated. Degaussing the biasing element along its length then again activates the tag.
In magnetizing, degaussing or changing the state of the biasing element of the aforesaid tags, care must be taken to prevent the magnetic field being used from extending beyond the tag into the merchandise. This can harm certain merchandise, particularly the above-mentioned prerecorded audio and video cassettes which are generally adversely affected by magnetic fields greater than 100 and 200 oersteds, respectively.
U.S. Pat. No. 4,752,758 to Heltemes discloses a demagnetizer used to degauss the biasing element of a harmonic tag so as to activate the tag. In the demagnetizer of the '758 patent, a magnetic sheet material is employed and is provided with successively magnetized sections along the length of the sheet. These sections alternate in magnetic polarity and decrease in intensity so that when a tag is moved along the length of the sheet its biasing element is degaussed. This patent also mentions that the alternating polarity regions are closely spaced to result in a rapid decrease in intensity of the field above the surface upon which the tag is moved so as not to adversely affect a magnetically sensitive object contained within the article carrying the tag.
The demagnetizer of the Heltemes patent provides an effective way of activating a harmonic EAS tag, while limiting the affect of the demagnetizer on articles by providing a degaussing field which decreases when moving away from the demagnetizer. However, the demagnetizer is not usable to deactivate (e.g., magnetize the biasing element of) a harmonic EAS tag, nor is it usable to activate a magneto-mechanical EAS tag.
It is, therefore, an object of the present invention to provide an improved apparatus for activating and/or deactivating a magneto-mechanical EAS tag and for deactivating a harmonic EAS tag.
It is a further object of the present invention to provide an apparatus meeting the above objective and which has a fast magnetic field falloff with distance, thereby limiting the penetration of the magnetic field into the merchandise carrying the tag.
It is a further object of the present invention to provide an improved apparatus meeting the above objectives and which is compact, simple in construction and economical to manufacture.